Many large valves (e.g., pigging valves) have removable closure caps. The weight of the closure cap becomes cumbersome as the size of the valve increases. For example, the closure cap on a twenty (20) inch diameter pigging valve cannot be removed without use of a davit system.
Generally, prior art davit systems use a single pillar davit system with a cantilever beam to open and support a closure cap. The weight of the closure cap for larger valves (e.g., larger than about twenty (20) inches in diameter) deforms the cantilever beam, making it difficult to align the closure cap with the valve properly.
Typically, closure caps are threaded. Misalignments between the closure cap and the valve can damage or gall the threads, causing the threads to freeze. Threaded closure caps also have other disadvantages. When opening (or closing) the valve, it takes time and effort to unthread (or thread) multiple turns of a cumbersome closure cap. Further, after continuous use under pressure, the threads could shear over time.
Thus, an improved valve system with a dual-pillar davit system and a threadless closure cap is needed to eliminate these problems.